1. Field of the Invention
The present invention relates to an abrasive roll and a method of producing the same.
2. Description of the Prior Art
It has hitherto been known that a method of producing an abrasive roll for use with rice polishing machines, for example, ordinarily comprises the step of forming a mixture of substances such as abrasive grains, a bond and a temporary caking agent, and that the formation of the mixture is effected, taking amounts or proportions of these respective substances into consideration. Also it has been known that a powder or a dust of substances such as polystyrene, foamed styrol, wood, cork and walnut is sometimes added into the mixture as a pore forming agent.
The abrasive roll produced without using the pore forming agent has a low porosity and suffers from an inferior polishing efficiency. When the grain percentage of an abrasive roll is increased with a view to attaining an improved polishing efficiency, the grade of the abrasive roll lowers. The abrasive roll having a low grade is impossible to be used for the rice polishing since partial wear thereof would occur during the polishing operation. Further, in the case where the powder or the dust of the abovementioned substances is used as the pore forming agent, it is difficult to enhance strength of the bond bridging and bonding the abrasive grains and hence to enhance the grade of the abrasive roll. The abrasive roll having the bond of low strength can be used for polishing rice at high efficiency only at an initial stage of the rice polishing operation. Since the strength of the bond and hence the grade are low, the bond may be broken, causing abrasive grains to be separated from the abrasive roll. This makes the surface portion of the abrasive roll rough and disadvantageously causes broken rice grains to be produced during the rice polishing.
The porosity of an abrasive roll may be increased by adjusting the molding pressure. However, the molding pressure adjustment is not effective for forming pores of uniform size and for preventing formation of pores of large size more than 500 .mu.m. The polishing with the use of the abrasive roll with the pores of such large size may disadvantageously cause the rice grains to be broken.